Spatial and temporal changes in shorebird habitats under different land use scenarios along the Yellow and Bohai Sea coasts in China

The effect of coastal wetland loss on shorebird habitat in recent years has been widely reported in previous studies. Various coastal wetland conservation and restoration measures have been implemented or will soon be implemented in China. The extent to which these measures will affect the area and structure of coastal wetland habitat in the future remains unclear. Here, we predicted changes in habitat area and structure for 39 common shorebird species along the coasts of the Yellow and Bohai Seas using a cellular automata-Markov (CA-Markov) land use scenario model and a maximum entropy species distribution model, along with terrain factors (slope, aspect, and digital evaluation model) and climate factors (temperature and precipitation) from the Data Centre for Resources and Environmental Sciences at the Chinese Academy of Sciences, land cover maps interpreted using the human-computer interactive method, and citizen science data of shorebird occurrences derived from eBird, Global Biodiversity Information Facility, and Bird Report. We found that shorebird habitat was most abundant along the coasts of Bohai Bay, Laizhou Bay, and Yancheng. The area of habitat decreased and became increasingly fragmented between 2000 and 2020 for more than half of the 39 species. Under the future business-as-usual scenario, the area of shorebird habitat decreased from 2020 to 2050, and the remaining habitat became increasingly fragmented. Under the ecological protection (EP) scenario, habitat loss was mitigated, and habitat connectivity was improved. The area of habitat was lower in 2050 under the EP scenario than in 2000 for most species, especially threatened species, suggesting that the area of habitat will not return to year-2000 levels under the EP scenario. These results emphasize the need to protect remaining shorebird habitats and implement ecological conservation measures to ensure the long-term preservation of coastal wetlands.

Nutrient dynamics in wetland systems associated with hydrological and anthropogenic variations in the south of Samborombón Bay, Argentina

Wetlands provide numerous ecosystem services to the environment, such as nutrient removal and storage. The aim of this work is to evaluate the nutrient dynamics in different sectors within wetland systems in the south of the Samborombón Bay (Argentina) based on hydrological and/or anthropogenic variations. For this purpose, the hydrological features of the wetland were defined through the analysis of satellite images, precipitation and tidal data, and field surveys. Three sectors were identified in the wetland: one with tidal influence, another which is dependent on rainfall, and another that receives inputs from rainfall and from a sewage effluent treatment plant. In order to analyze the nutrient dynamics, samples of surface water, groundwater, and sediments were collected from these sectors. Measurements of pH and electrical conductivity were determined in situ in water samples, while the concentration of inorganic forms of phosphorus and nitrogen, soluble reactive silica, and organic carbon were determined through laboratory analysis. Also, bioavailable phosphorus, organic matter, pH, and electrical conductivity were determined in the sediment samples collected. Statistical analysis of the data reveals differences between the sectors and allows the interpretation of the dynamics of the studied components in the wetland. Electrical conductivity distinguishes the intertidal sectors of the wetland while components associated with P and N discriminate the sectors with inputs from the sewage effluent treatment plant. On the other hand, soluble reactive silica, organic carbon, and organic matter do not seem to be influenced by the tide or effluent discharge. This study demonstrates that the studied wetland works as a nutrient retention area, providing ecosystem services to local inhabitants. Although these services can be utilized, they require a continuous monitoring over time to provide an early warning in case the variations in P and N cycles could lead to eutrophication or wetland degradation.

Effectiveness assessment of China's coastal wetland ecological restoration: A meta-analysis

Due to the coastal wetland degradation caused by human activities and environmental changes, many coastal wetland restoration studies have been carried out in China to restore the degraded ecosystems, but it still lacks a comprehensive assessment of restoration effectiveness at national scale. In this study, a meta-analysis of 78 field studies was conducted to quantitatively assess the restoration effectiveness of biodiversity and ecosystem services in China's coastal wetlands. At the same time, we evaluated the impact factors such as ecosystem types, restoration methods and measures, and restoration time on restoration effectiveness. The results show that coastal wetland ecological restoration has improved the biodiversity and ecosystem services by 36.8 % and 38.2 % respectively within the time range reported in the research literature, but neither has returned to the level of natural ecosystems. Biodiversity recovery is significantly positively correlated with the recovery of ecosystem services, indicating the simultaneous recovery outcome. Compared with degraded wetlands, the effectiveness of passive restoration is better than that of active restoration. In the mangrove ecosystem, invasive species removal is the most effective among the restoration measures, and the restoration effectiveness of polyculture plantations is better than that of monoculture plantations. When time ranges from 0 to 20 years, the recovery level of coastal wetlands tends to increase with the extension of restoration time. However, when the restoration time is >20 years, the recovery level decreases, which may be related to the lack of maintenance and management measures in the later stage. Our study showcases the scientific evidence for future coastal wetland ecological restoration in China.

Enhancing nutrient absorption through the influence of mangrove ecosystem on flow rate and retention time in salt marshes

This study investigates the impact of pneumatophores (the aerial roots of Avicenna marina) on water flow rate, retention time, contact time, and consequently on nutrient absorption through the sediment in sub-tropical salt marshes. The goal is to realize how the density of mangroves in salt marshes influences the kinematic factors of streamflow at estuaries. To this end, a field experiment was carried out to assess nutrient and organic compound levels in the sediment and water samples, spanning six sampling stations along the Chabahar River discharging to the Chabahar Bay, Iran. Then, we delved into the influence of altering environmental parameters, such as density and geometry, on the kinematic features of the flow through statistical analysis and hydraulic modeling. The results showed that the aerial roots reduce the flow rate and increase both retention and contact times. The longest retention time was observed at station #5 due to increased vegetation density and decreased instream velocity. In addition, measurements of total organic matter, total organic carbon, and total nitrogen indicated that an extended contact time resulted in increased absorption flux to the stream by sediments. As a result, pneumatophores can serve as an effective sink for organic matter in ecotones in salt marshes.

Coupling and decoupling of soil carbon and nutrients cycles at different salinity levels in a mangrove wetland: Insights from CUE and enzymatic stoichiometry

Soil carbon (C), nitrogen (N), and phosphorus (P) cycling, in conjunction with microbial metabolism, varies significantly with salinity in coastal areas. However, microbial metabolism limitation on salinity levels has received limited attention. Based on soil microbial carbon use efficiency and enzymatic stoichiometry, microbial nutrient limitation characteristics of soil microbial communities in different salinity levels (4.45 mS·cm-1 - 17.25 mS·cm-1) in a subtropical mangrove wetland were investigated. Compared to low-salinity levels, the activity of soil C-acquiring enzyme activities, enzymatic C:N ratios and enzymatic C:P ratios decreased with medium salinity levels and high salinity levels. Soil microbial metabolism was primarily constrained by C and N at different salinity levels. Boosted regression tree analysis revealed that abiotic factors had the greatest influence on C and N limitation of microbial metabolism at different salinity levels. This study underscores the significance of salinity in microbial metabolic processes and enhances our understanding of how future salinity changes induced by rising sea levels will affect soil carbon and nutrient cycling in coastal wetlands.

A framework to quantitatively assess the influence of land use and land cover on coastal wetland hydrological connectivity from a landscape resistance perspective

Land use and land cover (LULC) change is one of the dominant factors contributing to coastal wetland degradation and loss. Most studies focused on LULC changes or whether they influenced on ecosystems. However, few studies quantitatively assessed the impact of different LULCs on hydrological connectivity. This study aimed to understand how LULC affected hydrological connectivity in the coastal wetlands in the Yellow River Delta (YRD), China, from 1985 to 2020. A framework from a landscape resistance perspective was used to evaluate the LULC's influence. LULCs were converted into a series of resistance surfaces whose values represent the degree to which LULC facilitated or restricted hydrological connectivity. The LULC's influence was evaluated by parameterizing the resistance surfaces using observed hydrological connectivity. The results showed that human-related LULC had more influence on hydrological connectivity. The critical time of LULC's influence on hydrological connectivity was 1985-1990 and 2010-2015. The critical areas were Zone II, Zone I, and Zone VI. The LULCs of agriculture, industry, town/city, and river had the most significant impact on the hydrological connectivity of the YRD coastal wetland. The result could direct LULC planning to mitigate the negative effect on coastal wetlands and provide support for the environmental impact assessment of coastal development practices. This paper advances the study by assessing LULCs' impact on hydrological connectivity and providing a quantitative method. The framework of this study enriches the coastal wetland conservation theory and policy-making of coastal management.

Three thousand years of Hg pollution recorded in mangrove wetland sediments from South China

Mercury (Hg) is known to affect aquatic, terrestrial ecosystems as well as human health, through biomagnification. Mangrove wetlands are potential Hg sinks because of their low tidal velocity, fast sedimentation rate, strong reducing condition and high organic matter content. The spatial and temporal distribution of Hg has been a hot topic of recent studies in mangrove wetlands. In this study, we investigated Hg concentration, accumulation rate and isotopes to reconstruct the Hg pollution history and to differentiate its potential sources in the Gaoqiao mangrove wetland (Guangdong province), which is part of the largest mangrove area in China. We reconstructed a first, continuous, high-resolution Hg pollution history over the last 3000 years in South China. Our findings show that mangrove wetland sediments are more enriched in Hg than the adjacent grasslands. The increased Hg concentration and δ202Hg in recent sediments mirror the enhanced anthropogenic impacts; Hg concentrations in areas with high levels of anthropogenic disturbance are up to 5× higher than the average background value (9.9 ± 1.2 μg kg-1). Compared to mangroves in coastal areas of South China and around the world, the Hg concentration in Gaoqiao is much lower. The significant increase of Hg since the 1950s and the major Hg peak since the 1980s were the evidence of the human activities influences and indicated the possible start date of Anthropocene. After 2007 CE, a decline in Hg pollution occurs due to the effective implementation of the mangrove protection policy. Three potential sources were identified by the Hg isotope traces including urban gaseous Hg, industrial Hg, and regional soil and leaf litter Hg input.

Exploring the vulnerability of the coastal wetlands of India to the changing climate and their adaptation strategies

Changing climate exerts significant pressure on coastal wetland fishery, ecosystems and livelihood at the eco-regional level. In the present study, an indicator and scoring-based vulnerability assessment framework was developed to assess climate change-induced potential impacts and vulnerability of the coastal wetlands through stakeholder perception and primary data collection on ecology and fisheries. The study was conducted in 12 coastal wetlands in the Gangetic estuarine regions of eastern India. Analysis of rainfall, temperature and extreme climatic events was also carried out. The climate variability in the region was analysed and discussed in the context of ecosystem health and sustainability indicators. The results indicated that anthropogenic stress has a greater influence on ecosystem services than climatic stress. However, the nature and degree of vulnerability of fishers to climate change vary with their capacity to adapt to such changes and alternate sources of livelihood. Altogether, 34 fish species were documented, belonging to 11 taxonomic orders, and categorized as per intensity of resilience using selected criteria. Perception-based climate-resilient adaptation strategies have also been discussed. Developing appropriate adaptation policies and implementing climate-resilient practices and management can minimize vulnerability and increase the adaptive capacity of fishers ensuring sustainable livelihood options.

Residual effects of chlorinated organic pollutants on microbial community and natural redox processes in coastal wetlands

Chlorinated organic pollutants (COPs) are common in flooded environments. To examine the residual status and effects of COPs on flooded environments, a survey of 7 coastal wetlands in Zhejiang, East China was conducted. Total COP concentrations detected from 95.69 to 412.76 ng g-1 dw. Gamma-HCH and o,p'-DDT posed the greatest risk with exceedance rates of 100% according to sediment quality guidelines. Samples with higher COP pollution had higher microbial diversity, more complex microbial networks, more deterministic community assembly processes and lower microbiome stability, indicating an improved soil function for balance cycle of substances, especially for COP degradation. Further analysis using quantitative real-time PCR suggested COP-dechlorination interacted with natural redox processes, especially sulfate reduction and methanogenesis. The positive correlation between CH4 and pentachlorobenzene indicated a potential increase in greenhouse gas emissions caused by COP pollution. Correlation between dsr gene and COPs demonstrated the ability of sulfate-reducing bacteria to degrade COPs. Particularly, facultative OHRB such as sulfate-reducing bacteria hold significant importance in the process of COP-dechlorination. This finding provides a reference for COP pollution remediation. Collectively, our study offers new insight into the residual effect of COPs in coastal wetlands and contributes to an improved understanding of bioremediation strategies for COP pollution.

Polyethylene microplastic-induced microbial shifts affected greenhouse gas emissions during litter decomposition in coastal wetland sediments

Microplastic contamination has become increasingly aggravated in coastal environments, further affecting biogeochemical processes involved with microbial community shifts. As a key biogeochemical process mainly driven by microbiota in coastal wetland sediments, litter decomposition contributes greatly to the global greenhouse gas (GHG) budget. However, under microplastic pollution, the relationship between microbial alterations and GHG emissions during litter decomposition in coastal wetlands remains largely unknown. Here, we explored the microbial mechanism by which polyethylene microplastic (PE-MP) influenced greenhouse gas (i.e., CH4, CO2 and N2O) emissions during litter decomposition in coastal sediments through a 75-day microcosm experiment. During litter decomposition, PE-MP exposure significantly decreased cumulative CH4 and CO2 emissions by 41.07% and 25.79%, respectively. However, there was no significant change in cumulative N2O emissions under PE-MP exposure. The bacterial, archaeal, and fungal communities in sediments exhibited varied responses to PE-MP exposure over time, as reflected by the altered structure and changed functional groups of the microbiota. The altered microbial functional groups ascribed to PE-MP exposure and sediment property changes might contribute to suppressing CH4 and CO2 emissions during litter decomposition. This study yielded valuable information regarding the effects of PE-MP on GHG emissions during litter decomposition in coastal wetland sediments.

Increasing carbon and nutrient burial rates in mangroves coincided with coastal aquaculture development and water eutrophication in NE Hainan, China

Mangroves sequester and store large area-specific quantities of blue carbon (C) and essential nutrients such as nitrogen (N) and phosphorous (P). Quantifying C and nutrient burial rates in mangroves across a centennial time span and relating these rates to mangrove habitat is fundamental for elucidating the role of mangroves in carbon and nutrient budgets and their responses to environmental changes. However, relevant data are very limited in China. In this study, we used the radionuclides (210Pb and 137Cs) to determine chronologies and C, N and P burial rates in two mangrove forests located at different geomorphologic settings in NE Hainan Island, China. We found that the temporal patterns of C, N and P burial rates since 1900 fitted a quadratic function with a notable increase after 1960s in both mangroves, which coincided with the rapid development of coastal aquaculture since 1960s in NE Hainan and the subsequent coastal water eutrophication in this area. Sediment accretion rate (SAR) and mass accumulation rate (MAR) stayed relatively steady in the open-coastal mangroves, while they increased exponentially in the estuarine mangroves since 1900. The estuarine mangroves had significantly higher SAR and C, N and P burial rates than the open-coastal mangroves. C, N and P burial rates averaged at 141.52 g m-2 a-1, 6.27 g m-2 a-1 and 1.14 g m-2 a-1, respectively in the estuarine core, and these rates averaged at 61.71 g m-2 a-1, 3.71 g m-2 a-1 and 0.43 g m-2 a-1, respectively in the open-coastal core. The results suggest that estuarine mangroves may be more capable of surviving accelerating sea level rise under climate change and play a greater role in C accumulation and nutrient filtering under anthropogenic nutrient enrichment than marine-dominated mangroves. Blue C burial may be enhanced by coastal water eutrophication, but such a relationship needs to be tested in further studies.

The amelioration and improvement effects of modified biochar derived from Spartina alterniflora on coastal wetland soil and Suaeda salsa growth

Exotic species Spartina alterniflora (S. alterniflora) are widely invaded in the coastal zones of China and threaten the native ecosystem functions. In this study, phosphorus-magnesium modified BC (P-Mg modified BC) included PA-Mg-BC and DAP-Mg-BC derived from S. alterniflora were successfully prepared by co-pyrolysis of biomass and diammonium phosphate (DAP) or phosphoric acid (PA) and magnesium oxide (MgO). The preparation process markedly improved the surface morphologies, P loading amount, and P-containing functional groups of modified BC. The characterization results indicated that stable and low-solubility Mg-P complex formed on the surface of PA-Mg-BC and DAP-Mg-BC, which delayed the rapid release of P. Moreover, the MgO improved the buffering capacity of PA-Mg-BC and DAP-Mg-BC to competitive anions (SO42- and CO32-) during P release. Meanwhile, pot experiment showed that the suitable applications of PA-Mg-BC and DAP-Mg-BC could improve soil quality and fertility by enhancing SOC, DOC, TN, TP and AP contents, as well as β-glucosidase activities. The amended soil pH and salinity compared to the original soil also declined through precipitation and acid-base neutralization. In addition, P-Mg modified BC could improve bacterial community structure and promote the growth and biomass of Suaeda salsa (S. salsa). This study could provide a feasible method for realizing ecological restoration of coastal wetland and resource utilization of S. alterniflora.

Novel insight into the aging process of microplastics: An in-situ study in coastal wetlands

Coastal wetlands, the critical interface between the terrestrial and marine environments, provide a dynamic and unique environment for the aging of microplastics (MPs). Nevertheless, both abiotic and biotic processes that contribute to the aging of MPs in coastal wetlands have been largely neglected. In this study, the aging of MPs was continuously characterized in Hangzhou Bay, a representative coastal wetland in Zhejiang, China. Three-month exposure of polymers in sediment-water interface induced the aging phenomenon with embrittlement and exfoliation, as evidenced by simultaneous observed alternations in crystallinity and functional groups. A first-order kinetic model was fitted to describe the rate and degree of aging quantitatively. As evidenced by the carbonyl index, the residence time of all the examined MPs exhibited significant variance, ranging from 335 to 661 days. These variations might be caused by the selective attachment of plastic-degrading microorganisms (such as Moraxella sp. and Rhodococcus sp.). A positive correlation between the carbonyl index, the number of OTUs in the MP-associated biofilm, and irradiation was observed (p < 0.001), suggesting that the aging process may be co-regulated by natural sunlight and wetland microbial colonization. This study sheds new light on the long-term environmental fate of MPs and their associated ecological risks.

Effects of plastic contamination on carbon fluxes in a subtropical coastal wetland of East China

Coastal wetlands are recognized as carbon sinks that play an important role in mitigating global climate change because of the strong carbon uptake by vegetation and high carbon sequestration in the soil. Over the last few decades, plastic waste pollution in coastal zones has become increasingly serious owing to high-intensity anthropogenic activities. However, the influence of plastic waste (including foam waste) accumulation in coastal wetlands on carbon flux remains unclear. In the Yangtze Estuary, we investigated the variabilities of vegetation growth, carbon dioxide (CO2) and methane (CH4) fluxes, and soil properties in a clean Phragmites australis marsh and mudflat and a plastic-polluted marsh during summer and autumn. The clean marsh showed a strong CO2 uptake capacity (a carbon sink), and the clean mudflat showed a weak CO2 sink during the measurement period. However, polluted marshes are a significant source of CO2 emissions. Regardless of the season, the gross primary production and vegetation biomass of the polluted marshes were on average 9.5 and 1.1 times lower than those in the clean marshes, respectively. Ecosystem respiration and CH4 emissions in polluted marshes were significantly higher than those in clean marshes and mudflats. Generally, the soil bulk density and salinity in polluted marshes were lower, whereas the median particle size was higher at the polluted sites than at the clean sites. Increased soil porosity and decreased salinity may favor CO2 and CH4 emissions through gas diffusion pathways and microbiological behavior. Moreover, the concentrations of heavy metals in the soil of plastic-polluted marshes were 1.24-1.49 times higher than those in the clean marshes, which probably limited vegetation growth and CO2 uptake. Our study highlights the adverse effects of plastic pollution on the carbon sink functions of coastal ecosystems, which should receive global attention in coastal environmental management.

Effects of conversion of coastal marshes to aquaculture ponds on sediment anaerobic CO2 production and emission in a subtropical estuary of China

The extensive conversion of carbon-rich coastal wetland to aquaculture ponds in the Asian Pacific region has caused significant changes to the sediment properties and carbon cycling. Using field sampling and incubation experiments, the sediment anaerobic CO₂ production and CO₂ emission flux were compared between a brackish marsh and the nearby constructed aquaculture ponds in the Min River Estuary in southeastern China over a three-year period. Marsh sediment had a higher total carbon and lower C:N ratio than aquaculture pond sediment, suggesting the importance of marsh vegetation in supplying labile organic carbon to the sediment. Conversion to aquaculture ponds significantly decreased sediment anaerobic CO₂ production rates by 69.2% compared to the brackish marsh, but increased CO₂ emission, turning the CO₂ sink (-490.8 ± 42.0 mg m^-2 h^-1 in brackish marsh) into a source (6.2 ± 3.9 mg m^-2 h^-1 in aquaculture pond). Clipping the marsh vegetation resulted in the highest CO₂ emission flux (382.6 ± 46.7 mg m^-2 h^-1), highlighting the critical role of marsh vegetation in capturing and sequestering carbon. Sediment anaerobic CO₂ production and CO₂ uptake (in brackish marsh) and emission (in aquaculture ponds) were highest in the summer, followed by autumn, spring and winter. Redundancy analysis and structural equation modeling showed that the changes of sediment temperature, salinity and total carbon content accounted for more than 50% of the variance in CO₂ production and emission. Overall, the results indicate that vegetation clearing was the main cause of change in CO₂ production and emission in the land conversion, and marsh replantation should be a primary strategy to mitigate the climate impact of the aquaculture sector.

Effects of landscape modification on coastal sediment nitrogen availability, microbial functional gene abundances and N2O production potential across the tropical-subtropical gradient

Wetland sediment is an important nitrogen pool and a source of the greenhouse gas nitrous oxide (N₂O). Modification of coastal wetland landscape due to plant invasion and aquaculture activities may drastically change this N pool and the related dynamics of N₂O. This study measured the sediment properties, N₂O production and relevant functional gene abundances in 21 coastal wetlands across five provinces along the tropical-subtropical gradient in China, which all had experienced the same sequence of habitat transformation from native mudflats (MFs) to invasive Spartina alterniflora marshes (SAs) and subsequently to aquaculture ponds (APs). Our results showed that change from MFs to SAs increased the availability of NH₄⁺-N and NO₃^--N and the abundance of functional genes related to N₂O production (amoA, nirK, nosZ Ⅰ, and nosZ Ⅱ), whereas conversion of SAs to APs resulted in the opposite changes. Invasion of MFs by S. alterniflora increased N₂O production potential by 127.9%, whereas converting SAs to APs decreased it by 30.4%. Based on structural equation modelling, nitrogen substrate availability and abundance of ammonia oxidizers were the key factors driving the change in sediment N₂O production potential in these wetlands. This study revealed the main effect patterns of habitat modification on sediment biogeochemistry and N₂O production across a broad geographical and climate gradient. These findings will help large-scale mapping and assessing landscape change effects on sediment properties and greenhouse gas emissions along the coast.

Forecasting land-cover change effects on waterbirds in Xiamen Bay, China: Determining prospective species winners and losers

Waterbirds are vital to coastal wetland ecosystem, and play significant roles in global biodiversity maintenance, cultural and educational services, etc. Waterbirds are particularly vulnerable to environmental change, particularly land-cover change, which has severely degraded their ecological niches. Accordingly, this study developed a waterbird-habitat preference index to quantify waterbird dependence on Xiamen Bay's habitats and a subsidiary waterbird-specific habitat suitability index to predict potential effects of future land-cover change on waterbirds. Results showed that the waterbird-habitat preference index ranged from -9.8 to 18.71, indicating that habitat selection varied greatly among different waterbird species, where tidal flats were the most popular waterbird habitat. Additionally, most waterbird species showed a preference for more than one habitat, which could be indicative of their diverse ecological demands. Effects on waterbirds varied greatly among the three different land-cover scenarios, where positive benefits were predicted under the ecological protection scenario (EPS), while the greatest negative effects were observed under the development and utilization scenario (DUS). Effects also varied among different waterbirds species. Those under the current trend scenario (CTS) (e.g., Tringa brevipes and Calidris ruficollis) could be at risk for species abundance loss (i.e., losers) while others (i.e., Egretta garzetta and Saundersilarus saundersi) could benefit from increased abundance (i.e., winners). Generally, migratory and traveling birds were much more vulnerable than resident birds. Spatially, conservation priority should be given to the Dadeng Waters and those waters adjacent to it (i.e., Tongan Bay and Anhai Bay) because of the highest waterbird loss risk in these areas under a conflict between an urgent need to protect waterbird biodiversity and intense present and future land-cover development. The intent of this study is to provide a useful tool to explore land-cover effects on waterbirds in similar coastal regions, which can provide important information on protection and restoration strategies.

Effects of nitrogen and phosphorus supply levels and ratios on soil microbial diversity-ecosystem multifunctionality relationships in a coastal nontidal wetland

Human activities have changed the levels and ratios of nitrogen (N) and phosphorus (P) in wetland ecosystems. However, the effects of N and P levels and ratios on wetland soil microbial community and ecosystem multifunctionality remain unclear, especially on the relationships between soil microbial diversity and ecosystem multifunctionality. In this study, the effects of a 7-year experimental nutrient addition on the soil microbial community and ecosystem multifunctionality (12 function variables related to carbon, N, and P cycling) were assessed by combining three N and P supply levels with three N:P supply ratios in a coastal nontidal wetland ecosystem. According to the obtained results, the N and P supply levels significantly affected soil bacterial community composition, as well as ecosystem multifunctionality, while no significant effects of N:P supply ratios were observed. Although N and P supply levels did not significantly affect bacterial and fungal diversity, they both changed the complexity of bacterial and fungal networks. Soil ecosystem multifunctionality was significantly and positively correlated with bacterial diversity rather than fungal diversity. Moreover, the correlation coefficient between bacterial diversity and ecosystem multifunctionality showed an increasing-decreasing trend with increasing N and P supply levels and an increasing trend with increasing N:P supply ratios. However, the correlation coefficient between bacterial diversity and ecosystem multifunctionality was not significantly correlated with bacterial network complexity. The current study provides new insights into the impacts of N and P levels and ratios on soil microbial community and ecosystem multifunctionality in a coastal nontidal wetland. In particular, the present study highlighted that changes in N and P supply levels and ratios lead to changes in the relationship between soil bacterial diversity and ecosystem multifunctionality, which should be considered in related studies to accurately predict the responses of ecosystem multifunctionality to N and P inputs in coastal nontidal wetlands.

Invasive Spartina alterniflora habitat forms high energy fluxes but low food web stability compared to adjacent native vegetated habitats

Invasive Spartina spp. mostly colonizes a bare tidal flat and then establishes a new vegetated habitat, where it promotes the productivity of local ecosystems. However, it was unclear whether the invasive habitat could well exhibit ecosystem functioning, e.g. how its high productivity propagates throughout the food web and whether it thereby develops a high food web stability relative to native vegetated habitats. By developing quantitative food webs for a long-established invasive Spartina alterniflora habitat and adjacent native salt marsh (Suaeda salsa) and seagrass (Zostera japonica) habitats in China's Yellow River Delta, we investigated the distributions of energy fluxes, assessed the stability of food webs, and investigated the net trophic effects between trophic groups by combining all direct and indirect trophic interactions. Results showed that the total energy flux in the invasive S. alterniflora habitat was comparable to that in the Z. japonica habitat, whereas 4.5 times higher than that in the S. salsa habitat. While, the invasive habitat had the lowest trophic transfer efficiencies. Food web stability in the invasive habitat was about 3 and 40 times lower than that in the S. salsa and Z. japonica habitats, respectively. Additionally, there were strong net effects caused by intermediate invertebrate species in the invasive habitat rather than by fish species in both native habitats. This study revealed the contradiction between the promotion of energy fluxes and the decrease of food web stability resulting from the invasion of S. alterniflora, which provides new insights into the community-based management of plant invasions.

Microorganisms carrying nosZ I and nosZ II share similar ecological niches in a subtropical coastal wetland

Nitrous oxide (N₂O) reducers are the only known sink for N₂O and pivotal contributors to N₂O mitigation in terrestrial and water ecosystems. However, the niche preference of nosZ I and nosZ II carrying microorganisms, two divergent clades of N₂O reducers in coastal wetlands, is not yet well documented. In this study, we investigated the abundance, community structure and co-occurrence network of nosZ I and nosZ II carrying microorganisms and their driving factors at three depths in a subtropical coastal wetland with five plant species and a bare tidal flat. The taxonomic identities differed between nosZ I and nosZ II carrying microorganisms, with nosZ I sequences affiliated with Alphaproteobacteria and Betaproteobacteria while nosZ II sequences with Gemmatimonadetes, Verrucomicrobia, Gammaproteobacteria, and Chloroflexi. The abundances of nosZ I and nosZ II decreased with increasing soil depths, and were positively associated with salinity, total carbon (TC) and total nitrogen (TN). Random forest analysis showed that salinity was the strongest predictor for the abundances of nosZ I and nosZ II. Salinity, TC and TN were the major driving forces for the community structure of nosZ I and nosZ II carrying microorganisms. Moreover, co-occurrence analysis showed that 92.2 % of the links between nosZ I and nosZ II were positive, indicating that nosZ I and nosZ II carrying microorganisms likely shared similar ecological niches. Taken together, we provided new evidence that nosZ I and nosZ II carrying microorganisms shared similar ecological niches in a subtropical estuarine wetland, and identified salinity, TC and TN serving as the most important environmental driving forces. This study advances our understanding of the environmental adaptation and niche preference of nosZ I and nosZ II carrying microorganisms in coastal wetlands.

Salt marsh vegetation change during a half-century of experimental nutrient addition and climate-driven controls in Great Sippewissett Marsh

Vegetative cover was mapped annually, 1976-2022, in experimental plots in Great Sippewissett Marsh, Cape Cod, USA, chronically fertilized at different doses, and subject to changes in sea level and other climate-related variables. Dominant species within areas of higher elevation in the plots followed different decadal trajectories: rise in sea level diminished cover of Spartina patens; higher N supplies increased cover of Distichlis spicata. The opportunistic growth response of D. spicata to high N supplies unexpectedly fostered increased platform accretion, a feature that persisted for succeeding decades and led to further changes in vegetation: D. spicata functioned as an effective ecosystem engineer with long-term ecological consequences. Shrubs usually found in upper marsh margins expanded into areas where D. spicata had stimulated accretion, then shaded and excluded D. spicata, but subsequently lost cover as sea level rise continued. Increased N supply converted stands of Spartina alterniflora, the dominant low marsh species, from short to taller ecophenotypes; sea level rise had minor effects on S. alterniflora, but during 2019-2022 appeared to reach a tipping point that fostered taller S. alterniflora and bare space even in un-fertilized control plots, and in Great Sippewissett Marsh in general. Model results anticipate that-in spite of potential accretion enhanced by vegetation and ecosystem engineer effects-there will be loss of high marsh, transient increases of low marsh, followed by loss of low marsh, and eventual conversion to shallow open water by the end of the century. Dire local projections match those of the plurality of recent reports from salt marshes around the world. Proposed management strategies may only delay unfortunate outcomes rather than maintain wetlands. Concerted reductions of warming from greenhouse gases, and lower N loads seem necessary to address the coming crises in wetlands-and many other environmental threats.

Potential risk of co-occurrence of microplastics and chlorinated persistent organic pollutants to coastal wetlands: Evidence from a case study

Microplastic (MP) pollution in coastal wetlands is of a global concern. Little attention has been paid to the co-occurrence and corresponding risk of MPs with pollutants, especially refractory chlorinated persistent organic pollutants (CPOPs). A case study of Zhejiang, China was conducted to investigate the occurrence of MPs and targeted CPOPs in coastal wetlands. MPs were 100% detected, but with the lowest abundance in coastal wetlands (average: 666.1 ± 159.1 items kg^-1), as compared to other 6 terrestrial ecosystems (average: 1293.9 ± 163.7 items kg^-1) including paddy field, upland, facility vegetable field, forestland, urban soil, and grassland. A total of 35 kinds CPOPs were also detected in all studied coastal wetlands, with their concentration almost under 10 μg kg^-1 (90.1%). Both enrichment of MPs and CPOPs was affected by sediment TOC, wetland vegetation and land use simultaneously. Interestingly, the occurrence of MPs was significantly correlated with polychlorinated biphenyls (PCBs) but not organochlorine pesticides (OCPs). Results of co-occurrence pollution assessment of MPs and CPOPs further indicated only Hangzhou Bay showed the ecological risk among all tested wetlands. This would suggest a potential risk of co-occurrence of MPs and modern CPOPs in coastal wetland in economic development area. Possible reason may lie on strong MP vector effect to CPOPs. More attention should thus be paid to other wetlands polluted by MPs and MP-carrying CPOPs in area with relatively great environmental pressure induced by human activity. This study may provide reference for a better understanding with respect to the risk level posed by co-occurrence of MPs and CPOPs to global coastal wetlands.

A comparison of global mangrove maps: Assessing spatial and bioclimatic discrepancies at poleward range limits

Mangrove distribution maps are used for a variety of applications, ranging from estimates of mangrove extent, deforestation rates, quantify carbon stocks, to modelling response to climate change. There are multiple mangrove distribution datasets, which were derived from different remote sensing data and classification methods, and so there are some discrepancies among these datasets, especially with respect to the locations of their range limits. We investigate the latitudinal discrepancies in poleward mangrove range limits represented by these datasets and how these differences translate climatologically considering factors known to control mangrove distributions. We compare four widely used global mangrove distribution maps - the World Atlas of Mangroves, the World Atlas of Mangroves 2, the Global Distribution of Mangroves, the Global Mangrove Watch. We examine differences in climate among 21 range limit positions by analysing a set of bioclimatic variables that have been commonly related to the distribution of mangroves. Global mangrove maps show important discrepancies in the position of poleward range limits. Latitudinal differences between mangrove range limits in the datasets exceed 5°, 7° and 10° in western North America, western Australia and northern West Africa, respectively. In some range limit areas, such as Japan, discrepancies in the position of mangrove range limits in different datasets correspond to differences exceeding 600 mm in annual precipitation and > 10 °C in the minimum temperature of the coldest month. We conclude that dissimilarities in mapping mangrove range limits in different parts of the world can jeopardise inferences of climatic thresholds. We expect that global mapping efforts should prioritise the position of range limits with greater accuracy, ideally combining data from field-based surveys and very high-resolution remote sensing data. An accurate representation of range limits will contribute to better predicting mangrove range dynamics and shifts in response to climate change.

Substantial increase in P release following conversion of coastal wetlands to aquaculture ponds from altered kinetic exchange and resupply capacity

The reclamation of wetlands and its subsequent conversion to aquaculture may alter regional nutrient (im)mobilization and cycling, although direct assessments of phosphorus (P) cycling and its budget balance following wetland conversion are currently scarce. Here, parallel field experiments were conducted to investigate and compare the availability and mobilization mechanisms of P from natural coastal wetlands and the adjacent converted aquaculture ponds based on high-resolution diffusive gradient in thin films (DGT) and dialysis (HR-Peeper) techniques and the DGT-induced fluxes in sediments (DIFS) model. The study found that the conversion of wetland to pond strongly reduced the sediment P pool by changing its forms and distribution. High-resolution data showed that concentrations of labile P and soluble reactive P across the sediment-water profiles were markedly enhanced by the converted aquaculture pond, although they exhibited large spatiotemporal heterogeneity. Moreover, the synchronous distribution of labile P, iron (Fe) and sulfur (S) across profiles in coastal wetlands indicated that the dissolution of Fe (III) oxyhydroxide-phosphate complexes coupled with sulfate reduction were the main mechanisms regulating sediment P mobilization in coastal areas. However, the converted aquaculture pond weakened or even reversed this dependence by decoupling the Fe-S-P reactions by changing the sediment structure and nutrient balance. Substantial increases in labile P, Fe and S fluxes in the pond suggested the conversion of wetland to aquaculture facilitated the internal release of P, Fe and S from sediment into water. The high resupply parameter (R) and desorption rate (k_-1) combined with low response time (T_c) in the pond, as fitted by DIFS model, indicated the strong resupply capacity and fast kinetic exchange of sediment P across the sediment-water interface, which is consistent with the high P diffusion fluxes recorded in the pond. It was concluded that converted aquaculture ponds act as an important source of P release in coastal areas, potentially exacerbating water quality degradation and eutrophication. Specific initiatives and actions are therefore urgently needed to alleviate the internal P-loading during aquaculture.

Tracking of sea level impact on Caspian Ramsar sites and potential restoration of the Gorgan Bay on the southeast Caspian coast

The situation of Ramsar sites along the Caspian Sea coast has deteriorated over the past decades, and this is more noticeable in the narrow coastal strip of the south Caspian Sea. In this study we investigate how the Caspian Sea level changes affect the coastal Ramsar sites. Particularly, we focus on the Gorgan Bay in the southeast corner of the Caspian Sea, which is experiencing extensive water level decline, even desiccation. We used satellite images from three periods corresponding to periods of two sea level falls and one sea level rise, in order to decipher spatio-temporal changes of the wetlands. We conducted field campaign in the Gorgan Bay for sampling and measurement of physical, chemical and biological parameters. We simulated water circulation for the past, current and future conditions of the Gorgan Bay, which is essential to sustain better water exchange between the Bay and the Caspian Sea. We applied dust simulation in the case of a total desiccation of the Gorgan Bay. The result shows that the total area of the Caspian coastal Ramsar sites during the two periods of the sea level fall is almost the same; however, the aerial changes in the southern wetlands are more visible. Nutrient and plankton analysis of the Gorgan Bay display mainly mesotrophic conditions, in some areas close to eutrophic ones. The average current velocity in the main inlet is 2.5 cms^-1. Dust simulation indicates that in case of the Gorgan Bay desiccation, it will become a dust source for the surrounding area up to 60 km. Simulation of the water circulation with dredging of inlets (future scenario), indicates that the water exchange velocity doubles compared to the current scenario. A recommended inlet maintenance would accelerate water circulation and reduce residence time, which will lead to better trophy and prevent bay desiccation.

Soil salinity, not plant genotype or geographical distance, shapes soil microbial community of a reed wetland at a fine scale in the Yellow River Delta

Soil salinization is one of the most severe environmental problems restricting biodiversity maintenance and ecosystem functioning in a coastal wetland. Recent studies have well documented how salinization affects soil microbial communities along vegetation succession of coastal wetlands. However, the salinity effect is rarely assessed in the context of plant intraspecific variation. Here, we analyzed the soil bacterial and fungal communities of Phragmites australis wetland using amplicon high-throughput sequencing at a fine scale (within 1000 m) in the Yellow River Delta. Our results revealed that microbial diversity is significantly correlated to soil salinity (assessed as electrical conductivity, EC) but not to soil nutrients (N and P content) or plant intraspecific traits (leaf length, shoot height, and neutral genetic variation). Specifically, the microbial diversity tended to decrease with increased EC, and the bacterial community was more sensitive to EC change than the fungal community. The dominant bacterial phyla were Proteobacteria, Actinobacteria, and Chloroflexi, and the dominant fungal phyla were Ascomycota, Basidiomycota, and Mortierellomycota. The relative abundance of Actinobacteria was significantly negatively correlated to EC, while Proteobacteria were positively correlated to EC. In high salinity (> 1 mS/cm), the role of the stochastic processes became more important in community assembly according to habitat niche breadth estimation, neutral community model, C-score metric, and normalized stochasticity ratio. Additional common garden and microcosm experiments provided evidence that the genotype effect of P. australis on soil microbiome might only occur between lineages from different regions but not from the same region like the Yellow River Delta. Our findings provide new insights into soil microbial community assembly processes with the intraspecific variation of host plants in the wetland ecosystem and offer a scientific reference for salinity mitigation and vegetation management of coastal wetlands under future global changes.

Biogeochemical properties of blue carbon sediments influence the distribution and monomer composition of bacterial polyhydroxyalkanoates (PHA)

Coastal wetlands are highly efficient 'blue carbon' sinks which contribute to mitigating climate change through the long-term removal of atmospheric CO₂ and capture of carbon (C). Microorganisms are integral to C sequestration in blue carbon sediments and face a myriad of natural and anthropogenic pressures yet their adaptive responses are poorly understood. One such response in bacteria is the alteration of biomass lipids, specifically through the accumulation of polyhydroxyalkanoates (PHAs) and alteration of membrane phospholipid fatty acids (PLFA). PHAs are highly reduced bacterial storage polymers that increase bacterial fitness in changing environments. In this study, we investigated the distribution of microbial PHA, PLFA profiles, community structure and response to changes in sediment geochemistry along an elevation gradient from intertidal to vegetated supratidal sediments. We found highest PHA accumulation, monomer diversity and expression of lipid stress indices in elevated and vegetated sediments where C, nitrogen (N), PAH and heavy metals increased, and pH was significantly lower. This was accompanied by a reduction in bacterial diversity and a shift to higher abundances of microbial community members favouring complex C degradation. Results presented here describe a connection between bacterial PHA accumulation, membrane lipid adaptation, microbial community composition and polluted C rich sediments.

GRAPHICAL ABSTRACT

Geochemical, microbiological and polyhydroxyalkanoate (PHA) gradient in a blue carbon zone.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10533-022-01008-5.

Plant Species-Driven Distribution of Individual Clades of Comammox Nitrospira in a Subtropical Estuarine Wetland

Plant species play a crucial role in mediating the activity and community structure of soil microbiomes through differential inputs of litter and rhizosphere exudates, but we have a poor understanding of how plant species influence comammox Nitrospira, a newly discovered ammonia oxidizer with pivotal functionality. Here, we investigate the abundance, diversity, and community structure of comammox Nitrospira underneath five plant species and a bare tidal flat at three soil depths in a subtropical estuarine wetland. Plant species played a critical role in driving the distribution of individual clades of comammox Nitrospira, explaining 59.3% of the variation of community structure. Clade A.1 was widely detected in all samples, while clades A.2.1, A.2.2, A.3 and B showed plant species-dependent distribution patterns. Compared with the native species Cyperus malaccensis, the invasion of Spartina alterniflora increased the network complexity and changed the community structure of comammox Nitrospira, while the invasive effects from Kandelia obovata and Phragmites australis were relatively weak. Soil depths significantly influenced the community structure of comammox Nitrospira, but the effect was much weaker than that from plant species. Altogether, our results highlight the previously unrecognized critical role of plant species in driving the distribution of comammox Nitrospira in a subtropical estuarine wetland.

Improving cleaner production of human activities to mitigate total petroleum hydrocarbons accumulation in coastal environment

The marine coast is an important ecological transitional boundary but easily suffers from human intervention. Total petroleum hydrocarbons (TPHs) are ubiquitous along the coast. However, the influence of anthropogenic and natural factors on TPHs distribution remains unclear. This study sampled surficial sediment (N = 243) from the coasts of the largest peninsula-Leizhou Peninsula, in Southern China. We found that land-based discharge, sea traffic, and sediment type significantly (p < 0.05) drive the accumulation of TPHs. We observed that TPHs increased by 1.036 μg · g^-1 (exp[α_i] = exp. [0.0355]) of its original value with the addition of one more boat on the wharf. Although the average TPHs were at a moderate level (124.68, ND-1536.14, μg · g^-1) and risk, 'Blue Carbon' ecosystems, i.e., mangroves (224.84, ND - 1441.13, μg · g^-1, p < 0.001) were more severely polluted. Cleaner production policy should be applied to mitigate TPHs discharging trend from coastal areas.

Declines of methylmercury along a salinity gradient in a low-lying coastal wetland ecosystem at South Carolina, USA

Wetlands are widely regarded as biogeochemical hotspots of highly toxic methylmercury (MeHg), mainly mediated by sulfate-reducing bacteria. In low-lying coastal wetlands, sea level rise, a phenomenon caused by global climate change, is slowly degrading numerous healthy freshwater forested wetlands into salt-degraded counterparts with a nickname "ghost forests", and eventually converting them to saltmarshes. However, little is known about the changes of mercury (Hg) methylation, bioaccumulation, and biomagnification along the forest-to-saltmarsh gradient. Here, we conducted extensive field sampling in three wetland states (healthy forested wetlands, salt-degraded forested wetlands, and saltmarsh) along a salinity gradient (from 0 to 9.4 ppt) in Winyah Bay, South Carolina, USA. We found that in our study wetland systems the saltmarshes had the lowest levels of both total Hg and MeHg in sediments and biota, as compared to healthy forested wetlands and saltwater-degraded ghost forests. Our results suggest that the slow conversion of forested wetland to saltmarsh could reduce net MeHg production in our study wetland systems, which we hypothesized that could be attributed to increased sulfate reduction and excessive buildup of sulfide in sediment that inhibits microbial Hg methylation, and/or reduced canopy density and increased photodegradation of MeHg. However, it should be noted that biogeochemical MeHg responses to salinity changes may be site-specific and we urge more similar studies in other wetland systems along a salinity gradient. Therefore, long-term salinization of coastal wetlands and the slow conversion of forests to marshes could decrease long-term exposure of toxic MeHg levels in coastal food webs that are similar to our system, and ultimately reduce human exposure to this neurotoxin.

Invasion of Spartina alterniflora in the coastal zone of mainland China: Control achievements from 2015 to 2020 towards the Sustainable Development Goals

The Sustainable Development Goals (SDGs) and the Convention on Biological Diversity's 15th Conference of the Parties (CBD COP15) both emphasized the urgency of protecting biological diversity. Spartina alterniflora (S. alterniflora), as an invasive species in China, has posed severe biodiversity challenges, demanding nationwide control and management. This study aims to assess the effectiveness of S. alterniflora management during China's SDGs implementation from 2015 to 2020. Landsat images acquired in 2015 (the beginning year of SDGs), 2018, and 2020 (the end year of SDGs' targets 6.6, 14.2, 14.5, and 15.8 related to alien invasion) were applied to quantify the spatiotemporal dynamics of S. alterniflora extent. The results revealed a consistent shrinkage of S. alterniflora, with a net areal reduction of 2610 ha from 2015 to 2020, implying the effectiveness of control measures on S. alterniflora invasion. Provinces including Zhejiang, Jiangsu, and Shanghai have succeeded in controlling S. alterniflora, evidenced by the sharp reduction in S. alterniflora area by 4908 ha, 2176 ha, and 1034 ha, respectively, from 2015 to 2020. However, better management of S. alterniflora is needed in regions with more severe S. alterniflora invasion, e.g., Shandong, Fujian, and Guangdong provinces. Our results suggest that relevant policies, regulations, and ecological restoration projects implemented by national or local governments in China received satisfactory results in S. alterniflora control. Nevertheless, S. alterniflora potential utilities and its governance effectiveness should be objectively evaluated and weighed to obtain the greatest ecological benefits and promote sustainable coastal ecosystems. The results of this study are expected to provide important baseline information benefitting the formulation of coastal protection and restoration strategies in China.

Fingerprinting macrophyte Blue Carbon by pyrolysis-GC-compound specific isotope analysis (Py-CSIA)

There is a need for tools to determine the origin of organic matter (OM) in Blue Carbon Ecosystems (BCE) and marine sediments to (1) facilitate the implementation of Blue Carbon strategies into carbon accounting and crediting schemes and (2) decipher changes in ecosystem condition over decadal to millennial time scales and thus to understand and predict the stability of BCE in a changing world. Pyrolysis-GC-compound specific isotope analysis (Py-CSIA) is applied for the first time in marine environments and BCE research. We studied Australian mangrove, tidal marsh and seagrass sediments, in addition to potential sources of OM (Avicennia, Posidonia, Zostera, Sarcocornia, Ecklonia and Ulva species and seagrass epiphytes), to identify precursors of different biomacromolecule constituents (lignin, polysaccharides and aliphatic structures). Firstly, the link between bulk δ¹³C and δ¹³C reconstructed from compound-specific δ¹³C showed that the pyrolysis approach allows for the isotopic screening of a representative portion of the OM. Secondly, for all samples, the C isotope fingerprint of the carbohydrate products (plant polysaccharides) was the heaviest (¹³C enriched), followed by lignin and aliphatic products. The differences in δ¹³C among macromolecules and the overlap in δ¹³C among putative sources reflect the limitations of bulk δ¹³C analyses for deciphering OM provenance. Thirdly, phanerogams specimen had the heaviest carbohydrate and lignin, confirming that seagrass-derived lignocellulose can be traced based on δ¹³C. Consistent differences for individual compounds were identified between seagrasses and between Avicennia and Sarcocornia using Py-CSIA. Fourth, ecosystem shifts (colonization of seagrass habitats by mangrove) on millenary time scales, hypothesized in previous studies on the basis of bulk δ¹³C and Py-GC-MS, were confirmed by Py-CSIA. We conclude that Py-CSIA is useful in Blue Carbon research to decipher OM sources in marine sediments, identify ecosystem transitions in palaeoenvironmental records, and to understand the role of different OM compounds in Blue Carbon storage.

Large increase in CH4 emission following conversion of coastal marsh to aquaculture ponds caused by changing gas transport pathways

Methane emissions from aquatic ecosystems play an important role in global carbon cycle and climate change. Reclamation of coastal wetlands for aquaculture use has been shown to have opposite effects on sediment CH₄ production potential and CH₄ emission flux, but the underlying mechanism remained unclear. In this study, we compared sediment properties, CH₄ production potential, emission flux, and CH₄ transport pathways between a brackish marsh and the nearby reclaimed aquaculture ponds in the Min River Estuary in southeastern China. Despite that the sediment CH₄ production potential in the ponds was significantly lower than the marsh, CH₄ emission flux in the ponds (17.4 ± 2.7 mg m^-2 h^-1) was 11.9 times higher than the marsh (1.3 ±  0.2 mg m^-2 h^-1). Plant-mediated transport accounted for 75% of the total CH₄ emission in the marsh, whereas ebullition accounted for 95% of the total CH₄ emission in the ponds. CH₄ emission fluxes in both habitat types were highest in the summer. These results suggest that the increase in CH₄ emission following the conversion of brackish marsh to aquaculture ponds was not caused by increased sediment CH₄ production, but rather by eliminating rhizospheric oxidation and shifting the major transport pathway to ebullition, allowing sediment CH₄ to bypass oxidative loss. This study improves our understanding of the impacts of modification of coastal wetlands on greenhouse gas dynamics.

An evaluating system for wetland ecological risk: Case study in coastal mainland China

Coastal wetland degradation and fragmentation contribute to habitat and biodiversity loss. We construct wetland ecological risk assessment framework to evaluate the risk posed to 35 coastal wetland national nature reserves (NNRs) in China for the years 2000 and 2020. Our wetland ecological risk index (WRI) is based on an external hazard sub-index (EHI) and an internal vulnerability sub-index. Most NNRs have low EHI values in both 2000 and 2020. Ratios of change in EHI range from -22.76% to 52.15% (a negative value indicates a decrease, a positive value an increase), and the EHI for 20 of 35 NNRs (57.1%) decreases over time. Variation in the internal vulnerability index ranges -44.78% to 88.97%, and increases at 18 NNRs (51.4%) over time. WRI variation ranges between -48.13% and 82.91%, and increases at 19 NNRs (54.3%). Most NNRs are ranked as being at low, medium risk in both 2000 and 2020. Notably, the number of high-risk NNRs increases from 3 to 10 (for which WRI values also increase). Expansion of built-up land, cropland occupation (in 2020), road disturbance, and water quality are all significantly associated WRI. Intensified management of the 10 NNRs ranked at high risk is necessary to prevent further deterioration.

Denitrifying anaerobic methane oxidation and mechanisms influencing it in Yellow River Delta coastal wetland soil, China

Methane oxidation coupled to denitrification is mediated by Candidatus "Methylomirabilis oxyfera" (M. oxyfera), which belongs to the candidate phylum NC10, and plays a crucial role in the global carbon and nitrogen cycle. Using the Yellow River Delta coastal wetland as the study area, molecular biology technology and laboratory incubation were used to determine the abundance of NC10 bacteria and the denitrifying anaerobic methane oxidation (DAMO) rate in soils from different vegetation areas. The results of the electrophoresis detection show that M. oxyfera-like bacteria can be found in the four types of soils, according to the growth analysis by the system, OTU1 (SA) has been found the highest similarity to first-discovered Candidatus Methylomir-abilis oxyfera (FP565575) (over 98%); Vegetation cover significantly increased the abundance of M. oxyfera-like bacteria compared to beach areas, which abundance was significantly higher in deeper layers than in surface ones. Nitrate, nitrite, total nitrogen, and conductivity were identified as the main environmental factors affecting the DAMO rate. This study showed that both groups A and B of Candidatus M. oxyfera-like bacteria exist in the coastal wetland of the Yellow River Delta, which provides molecular biological evidence for the existence of the DAMO process therein. Moreover, it was revealed the influence mechanism of physical and chemical characteristics of each region on the DAMO rate. This is of significance for furthering our understanding of the coupled effect of the global carbon and nitrogen cycle.

Nitrogen input promotes denitrifying methanotrophs' abundance and contribution to methane emission reduction in coastal wetland and paddy soil

Denitrifying anaerobic methane oxidation (DAMO) microorganisms, using nitrate/nitrite to oxidize methane, have been proved to be an important microbial methane sink in natural habitats. Increasing nitrogen deposit around the globe brings increased availability of substrates for these microorganisms. However, how elevated nitrogen level affects denitrifying methanotrophs has not been elucidated. In this study, sediment/soil samples from coastal wetland with continuous nitrogen input and paddy field with periodic nitrogen input were collected to investigate the influence of nitrogen input on the abundance and activity of denitrifying methanotrophs. The results indicated that nitrogen input significantly promoted DAMO microorganisms' abundance and contribution to methane emission reduction. In the coastal wetland, the contribution rate of DAMO process to methane removal increased from 12.1% to 33.5% along with continuously elevated nitrogen level in the 3-year tracking study. In the paddy field, the DAMO process accounted for 71.9% of total methane removal when nitrogen fertilizer was applied during the growing season, exceeding the aerobic methane oxidation process. This work would help us better understand the microbial methane cycle and reduce uncertainties in the estimations of the global methane emission.

Spartina alterniflora invasion has a greater impact than non-native species, Phragmites australis and Kandelia obovata, on the bacterial community assemblages in an estuarine wetland

The invasion of Spartina alterniflora poses a serious threat to the sustainability of native ecosystems worldwide. However, compared with other non-native plants (e.g., Phragmites australis and Kandelia obovata), how Spartina alterniflora invasion influences the community structure of bacteria and their assembly processes and functionality remains elusive. Here, we characterized the diversity, community structure, assembly processes and functional guilds of bacteria underneath five plant species and a bare tidal flat at three soil depths in an estuarine wetland. We found that plant species played a more important role than soil depth in mediating the bacterial community structure. Compared with bare tidal flats, the native species Cyperus malaccensis, rather than Scirpus triqueter, significantly changed the bacterial community structure. However, S. alterniflora invasion increased bacterial alpha diversity and significantly altered the bacterial community structure by enriching Chloroflexi, Bacteroidetes and Firmicutes while reducing Acidobacteria, Nitrospirae and Gemmatimonadetes. The invasion of P. australis and translocation of K. obovata had less pronounced effects on the bacterial community structure. Total carbon, total nitrogen and salinity were the key environmental factors mediating the bacterial community structure. Overall of all the non-native plant species, the invasion of S. alterniflora increased the relative importance of stochastic processes in the assembly of bacterial communities, and shifted the bacterial functional profiles by stimulating sulfur cycling groups and suppressing nitrogen cycling groups. Altogether, our results suggest that S. alterniflora invasion has a greater effect than P. australis invasion or K. obovata translocation on the profiles and assembly processes of the bacterial communities, with important implications for soil biogeochemical processes in coastal wetlands.

Estimating the recreational value of a coastal wetland park: Application of the choice experiment method and travel cost interval analysis

Estimating the recreational value of a coastal wetland park is useful in understanding wetland ecosystem and nurturing a balanced relationship between wetland tourism exploration and natural conservation. This study aims to apply appropriate methodologies to accurately estimate the recreational value of a coastal wetland park. The Nansha Wetland in China was used as the study site, and its recreational value was divided into non-use value (estimated using the choice experiment method (CEM)) and use value (estimated using travel cost interval analysis (TCIA)). The data were collected via questionnaires consisting of different choice experiment scenarios and travel cost investigations. The results showed that the per capita and total non-use values were 116.97 CNY/17.80 USD and 24.56 million CNY/3.74 million USD, respectively, and the per capita and total use values were 313.95 CNY/47.79 USD and 65.93 million CNY/10.04 million USD. Therefore, the per capita and total recreational values were 430.92 CNY/65.59 USD and 90.49 million CNY/13.77 million USD. CEM was used to identify tourists' trade-offs and preferences among the selected wetland attributes. As a result, tourists were found to have the largest marginal willingness to pay (MWTP) for "mangrove coverage," followed by "species of rare birds" and "water visibility." TCIA was used to solve the under-dispersion problem of the number of trips. Based on these findings, several managerial implications were identified, including adjusting ticket price based on the non-use value, regulating tourists' behaviors, enhancing the protection of mangroves, improving the water quality and the living habitats of migrant birds, and promoting science education and popularization.

Heavy metal pollution in coastal wetlands: A systematic review of studies globally over the past three decades

Coastal wetlands are ecosystems lying between land and ocean and are subject to inputs of heavy metals (HMs) from terrestrial, oceanic and atmospheric sources. Although the study on HM pollution in coastal wetlands has been rapidly developing over the past three decades, systematic reviews are still unavailable. Here, by analyzing 3343 articles published between 1990 and 2019, we provided the first holistic systematic review of studies on HM pollution in coastal wetlands globally. The results showed a trend of rapid increases in publications in this field globally, especially over the past ten years. Trends varied greatly among coastal countries, and global trends were primarily driven by the US before 2000, and in China after 2010. We also found that mercury (Hg), cadmium (Cd), and copper (Cu) were the most widely studied HM elements globally, but patterns differed geographically, with Hg being most widely examined in the Americas, Cd in China and India, and lead (Pb) in the western Europe and Australia, respectively. Among different types of coastal wetlands, salt marshes, mangrove forests, and estuaries were the most widely studied, in contrast to seagrass beds and tidal flats. As for ecosystem components, soils/sediments and plants were most extensively investigated, while algae, microbes, and animals were much less examined. Our analysis further revealed rapid emergence of topics on anthropogenic sources, interactions with other anthropogenic environmental changes (climate change in particular), and control and remediation methodology in the literature in the recent ten years. Moving forward, we highlight that future studies are needed to i) better understand the impacts of HM pollution in less studied coastal wetland systems and species, ii) deepen current understanding of the biogeochemical behaviors of HMs under anthropogenic activities, iii) examine interactions with other anthropogenic environmental changes, iv) conceive ecological remediation (i.e., "ecoremediation" as compared to traditional physiochemical remediation and bioremediation) strategies, and v) develop advanced analysis instruments and methods. The perspectives we brought forward can help stimulate many new advances in this field.

A Conterminous USA-Scale Map of Relative Tidal Marsh Elevation

Tidal wetlands provide myriad ecosystem services across local to global scales. With their uncertain vulnerability or resilience to rising sea levels, there is a need for mapping flooding drivers and vulnerability proxies for these ecosystems at a national scale. However, tidal wetlands in the conterminous USA are diverse with differing elevation gradients, and tidal amplitudes, making broad geographic comparisons difficult. To address this, a national-scale map of relative tidal elevation (Z*_MHW), a physical metric that normalizes elevation to tidal amplitude at mean high water (MHW), was constructed for the first time at 30 × 30-m resolution spanning the conterminous USA. Contrary to two study hypotheses, watershed-level median Z*_MHW and its variability generally increased from north to south as a function of tidal amplitude and relative sea-level rise. These trends were also observed in a reanalysis of ground elevation data from the Pacific Coast by Janousek et al. (Estuaries and Coasts 42 (1): 85-98, 2019). Supporting a third hypothesis, propagated uncertainty in Z*_MHW increased from north to south as light detection and ranging (LiDAR) errors had an outsized effect under narrowing tidal amplitudes. The drivers of Z*_MHW and its variability are difficult to determine because several potential causal variables are correlated with latitude, but future studies could investigate highest astronomical tide and diurnal high tide inequality as drivers of median Z*_MHW and Z*_MHW variability, respectively. Watersheds of the Gulf Coast often had propagated Z*_MHW uncertainty greater than the tidal amplitude itself emphasizing the diminished practicality of applying Z*_MHW as a flooding proxy to microtidal wetlands. Future studies could focus on validating and improving these physical map products and using them for synoptic modeling of tidal wetland carbon dynamics and sea-level rise vulnerability analyses.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12237-021-01027-9.

Distribution, sources, and ecological risk assessment of polycyclic aromatic hydrocarbons (PAHs) in the tidal creek water of coastal tidal flats in the Yellow River Delta, China

The concentrations, distribution, sources and ecological risk levels of polycyclic aromatic hydrocarbons (PAHs) in tidal creek water from coastal tidal flats of the Yellow River Delta were investigated. The concentrations of 16 PAHs ranged from 0.113 to 1.533, with a mean value of 0.496 ± 0.035 μg L^-1, which indicated a moderate level of pollution. The main long-term sources of PAHs in the coastal tidal flats of the Yellow River Delta were petroleum combustion and petroleum pollution. The ecological risk assessment showed that the levels of PAHs in tidal creek water of the coastal tidal flats in the Yellow River Delta corresponded to medium to high ecological risk levels, and a high probability of potential ecological risk, posing harm to aquatic organisms. Among the 7 sampling sites, site 5, site 6, and site 7 were at high ecological risk, and the other sites were at moderate ecological risk. PAH pollution in the tidal creek water near the Yellow River Estuary and farther south, in the coastal tidal wetland of Laizhou Bay, deserves special attention, especially with respect to the prevention and control of benzo[a]pyrene (BaP) pollution in the water.

Vegetation successions of coastal wetlands in southern Laizhou Bay, Bohai Sea, northern China, influenced by the changes in relative surface elevation and soil salinity

Vegetation successions of coastal wetlands were influenced by the changes in relative surface elevation and soil salinity. In this study, the vegetation successions of coastal wetlands in southern Laizhou Bay and the factors influencing the successions were investigated by quadrat survey. The changes of relative surface elevation and soil salinity in coastal wetlands of the study region were caused by climate change, sea-level rise, coastal erosion, sedimentation, neotectonism, storm surge, seawater intrusion, invasion of Spatina alterniflora, and utilization of underground brine. The changes led to the regressive vegetation succession of coastal wetlands without the protection of sea embankment and the progressive vegetation succession of coastal wetlands with the protection of sea embankment. The invasion of S. alterniflora resulted in the regressive vegetation succession of wetlands in the riparian zone. The successions weakened the coastal wetlands' ecological capacities of carbon sequestration, pollutant purification, and resisting marine disasters, decreasing their species diversity. Some measures were proposed to resist the adverse impact of successions, such as introducing passenger water, storing water in flood season, digging 200 hm² of ponds, and planting Salix matsudana and Tamarix chinensis around the ponds.

Unraveling bacterial community structure and function and their links with natural salinity gradient in the Yellow River Delta

Salinization can change the soil environment and affect microbial processes. In this study, soil samples were collected from Zone A (Phragmites australis wetlands), Zone B (P. australis and Suaeda salsa wetlands), and Zone C (Spartina alterniflora wetlands) in the Yellow River Delta. The microbial community and functional potential along the natural salinity gradient were investigated. Total nitrogen, ammonia nitrogen, and soil organic matter presented a downward trend, and salinity first increased and then decreased from Zone A to Zone C. Nitrospira and norank_f_Nitrosomonadaceae were widely distributed throughout the zones. Denitrifying bacteria Alcanivorax, Marinobacterter, and Marinobacterium were abundant in Zone B and preferred high salinity levels. However, denitrifying bacteria Azoarcus, Flavobacterium, and Pseudomonas were mainly distributed in low-salinity Zones A and C, suggesting their high sensitivity to salinity. Dissimilatory nitrate reduction to ammonia (DNRA) bacteria Aeromonas and Geobacter dominated Zone C, whereas Caldithrix performed DNRA in Zone B. Interestingly, DNRA with organic matter as the electron donor (C-DNRA) occurred in Zone A; DNRA coupled with sulfide oxidation (S-DNRA) was dominant in Zone B; and C-DNRA and DNRA with divalent iron as electron donor and S-DNRA occurred simultaneously in Zone C. Salinity was the key factor distinguishing low and high salinity zones, and total nitrogen and total phosphorus had important effects at the phylum and genus levels. The abundance of genes encoding cell growth and death was relatively stable, indicating that the microbial community had good environmental adaptability. The genes related to the biodegradation of xenobiotics and the metabolism of terpenoids and polyketides were abundant in Zone B, revealing high metabolic potential for exogenous refractory substances. The microorganisms under low-salinity Zones A and C were more sensitive to environmental changes than those under Zone B. These results suggest that salinity plays important roles in microbial processes and shapes specific functional zones in coastal wetlands.

Top-down control of foundation species recovery during coastal wetland restoration

Restoration has been increasingly adopted to halt trends in coastal wetland loss globally. Existing restoration often assumes that once abiotic stress is relieved, disturbances are prevented, and invasive species are eradicated, coastal wetlands will recover if propagules of native species are supplied either through natural dispersal or planting. Whether other factors including consumers can help explain the often suboptimal performance of existing restoration remains poorly understood. In a series of field experiments in the Yangtze estuary, we examined the relative importance of abiotic stress and crab grazing in regulating the recovery of the native foundation plant species Scirpus mariqueter in salt marsh areas where exotic cordgrass was successfully eradicated. We found that grazing by herbivorous crabs, rather than abiotic stress, was the primary obstacle restricting the recovery of planted Scirpus. This negative effect of crab grazing varied predictably across elevation and was strongest at low elevations where abiotic conditions were positive for Scirpus. These findings highlight that i) measures to control crab grazing are needed to enhance the success of Scirpus restoration, even in areas where abiotic conditions are set to be optimal, and ii) restoration measures purely focused on reducing abiotic stress could be ineffective or suboptimal in field conditions, likely jeopardizing restoration investment and success. Since top-down control of foundation plant species is common in many coastal wetlands and can be especially important in degraded systems where herbivores are abundant, we urge that future coastal wetland restoration assesses for the impacts of grazers and, when present, apply intervention measures.

Interactive effects of crab herbivory and spring drought on a Phragmites australis-dominated salt marsh in the Yellow River Delta

Consumers are often overlooked as key drivers of vegetation structure and ecosystem functioning in coastal wetlands. This oversight is particularly apparent in Asia, where much of the variation in coastal wetland plant growth and composition is attributed to physical stress gradients. To address this knowledge gap and quantify the relative importance of consumers in Asian coastal wetlands across temporal variation in environmental stress, we conducted a two-year experiment spanning relatively spring wet (2018) and spring dry (2019) years in which we manipulated the presence of the numerically dominant herbivorous crab, Helice tientsinensis, and evaluated its effects on Phragmites australis growth and structure in a Yellow River Delta salt marsh. In spring wetter 2018, Phragmites biomass and stem density were 75% and 34% higher in Crab Exclusion relative to Ambient Crab plots. In 2019 which experienced spring drought and elevated soil salinity, Phragmites biomass and stem density remained similarly high relative to 2018 in Crab Exclusion plots, but fell further, to only 16% and 39% of levels of 2018 observed in Ambient Crab plots. Phragmites' inflorescences density was also significantly reduced in Ambient Crab than Crab Exclusion plots in 2019. Together, these results highlight the significant role that crab herbivores can play in regulating Phragmites in Yellow River Delta salt marshes and suggest that the magnitude of their top-down control may be amplified, although in a non-additive manner, with spring drought stress in the region.

Intertidal wetland vegetation dynamics under rising sea levels

Intertidal wetlands have historically been in decline and are increasingly at risk due to climate change, particularly sea level rise (SLR). Different intertidal wetland communities can adapt to SLR via lateral upslope retreat to higher ground, capture and accumulation of allochthonous sediment, and/or organic accretion. In this paper, a case study is presented to assess the impact of the overall sediment accretion rate (i.e. allochthonous and organic accumulation) versus possible SLR rates on wetland species composition. Initially, an eco-hydraulic calculation method is developed to estimate existing spatial and temporal tidal inundation statistics of saltmarsh species at a Ramsar listed wetland on the south-east coast of New South Wales, Australia. SLR and accretion scenarios were then tested using high resolution hydrodynamic models to predict future saltmarsh species composition based on the eco-hydraulic calculation method. Saltmarsh species composition and extents were found to persist if sea levels continue to rise at present-day rates, as observed rates of SLR are similar. However, if the SLR rate accelerates beyond the accretion ability of the wetland, a significant shift in species composition and an increase in open water coverage was predicted. These results indicate that the current rate of sediment capture by wetland species, and the subsequent rate of elevation change, will need to increase significantly to adapt with projected future rates of SLR.

Effect of inundation on greenhouse gas emissions from temperate coastal wetland soils with different vegetation types in southern Australia

Predicted sea level fluctuations and sea level rise with climate change will lead to inundation of coastal and estuarine soils. Coastal wetlands usually contain large amounts of organic matter, which can be potential sources of greenhouse gas emissions (GHGs; CO₂, CH₄, N₂O) during decomposition, but there are limited studies on the effects of sea level variation on GHGs in coastal wetlands. We measured the effect of brackish water inundation and wetting and drying cycles on GHG emissions from coastal wetland soil cores that supported four different vegetation types: Apium gravedens (AG), Leptospermum lanigerum (LL), Phragmites australis (PA) and Paspalum distichum (PD) from the estuarine floodplain of the Aire River in south-western Victoria, Australia. Intact soil cores were incubated under either dry, flooded, or a 14 day wet-dry cycle treatments for a total of 56 days at a constant temperature of 23 °C. CO₂, CH₄, and N₂O fluxes were investigated in closed chambers and measured with gas chromatography. In the dry treatment, a positive correlation was found between soil organic carbon (SOC) and CO₂ flux, and between SOC and CH₄ flux. Higher SOC is indicative of higher amounts of soil organic matter (SOM) which acts as a source of substrate for microbes to produce CO₂ or CH₄ emissions under aerobic or anaerobic conditions. The NO₂^- and NO₃^- concentrations were positively correlated with N₂O emissions in the wet-dry cycle treatment. NO₂^- and NO₃^- provide a supply of substrate for denitrification. The flooded treatment decreased cumulative CO₂ emissions by 34%, 25% and 14% at the LL, PA, PD sites, respectively, and decreased cumulative N₂O emissions by 42%, 39% and 43% at the AG, LL and PA sites, compared to the dry treatment. The wet-dry cycle treatment and dry treatment decreased cumulative CH₄ emissions for all vegetation types compared to the flooded treatment. The redox potential (Eh) was negatively correlated with CH₄ flux and positively correlated N₂O flux at all sites. This study highlights the significance of sea level fluctuations when estimating GHG flux from coastal and estuarine floodplains which are highly vulnerable to inundation, and the role of SOC and mineral N as important drivers affecting GHG flux.

Soil organic matter and salinity as critical factors affecting the bacterial community and function of Phragmites australis dominated riparian and coastal wetlands

Soil salinization poses a great threat to the natural ecosystem and interferes with the structure and function of the biological community, resulting in different vegetation distributions. However, little attention is paid to the changes in microbial community in different wetland types with the same vegetation. In this study, the Yellow River Delta was used as a model because of its typical and extensive distribution of Phragmites australis-dominated saltwater and freshwater wetlands. We investigated the differences in the structure and function of bacterial communities, as well as their relationships with soil properties in coastal (Zone A) and riparian (Zone B) wetlands. Results showed higher salinity and pH in Zone A than Zone B (p < 0.05), whereas TN (p < 0.05) and SOM were lower than those in Zone B. Significant differences existed in microbial community composition between Zones A and B. The nitrifying-bacteria Nitrospira and norank_f_Nitrosomonadaceae had high abundance in Zones A and B. Alcanivorax, Halomonas, and Marinobacter were extensively distributed in Zone A, whereas Flavobacterium and Pseudomonas were dominant in Zone B, indicating the diversity characteristics of denitrifying bacteria. Conversely, methane-oxidizing bacteria Methylophaga were significantly higher in Zone A than in Zone B (p < 0.05), indicating that high salinity was conducive to aerobic methane oxidation and that the genetic diversity at strain level endowed it with a certain denitrification potential. Salinity and SOM played important roles in shaping microbial community at phylum and genus levels. The gene abundances related to xenobiotics metabolism and repair were high in Zone A, whereas the genes encoding energy metabolism and signal transduction were relatively high in Zone B. Denitrification was more favored for the low-salinity Zone B, whereas methane oxidation was enriched in the high-salinity Zone A. Therefore, our study emphasized the importance of an in-depth understanding of the microbial-community structure and function in Phragmites australis-dominated saltwater and freshwater wetlands.

Salinity and nutrient modulate soil bacterial communities in the coastal wetland of the Yellow River Delta, China

The Yellow River Delta is the largest and youngest estuarine and coastal wetland in China and is experiencing the most active interactions of seawater and freshwater in the world. Bacteria played multifaceted influence on soil biogeochemical processes, and it was necessary to investigate the intermodulation between the soil factors and bacterial communities. Soil samples were collected at sites with different salinity degree, vegetations, and interference. The sequences of bacilli were tested using 16S rRNA sequencing method and operational taxonomic units were classified with 97% similarity. The soil was highly salinized and oligotrophic, and the wetland was nitrogen-restricted. Redundancy analysis suggested that factors related with seawater erosion were principal to drive the changes of soil bacterial communities and then the nutrient level and human disturbance. A broader implication was that, in the early succession stages of the coastal ecosystem, seawater erosion was the key driver of the variations of marine oligotrophic bacterial communities, while the increasing nutrient availability may enhance in the abundance of the riverine copiotrophs in the late stages. This study provided new insights on the characteristics of soil bacterial communities in estuarine and coastal wetlands.

Is there evidence of local adaptation of Phragmites australis to water level gradients and fluctuation frequencies?

Greater differences in hydrologic conditions are expected between coastal and inland wetlands with global climate change. Local adaptation has been considered as a significant driver of intraspecific differentiation in heterogeneous habitats. The common reed Phragmites australis is a cosmopolitan wetland species with high genetic variability and adaptability. In our study, reeds collected from coastal and inland wetlands were subjected to three stable water level gradients and two fluctuation frequencies in a common garden experiment. We measured their aboveground and belowground biomass, height, density, stem diameter, leaf water potential, specific leaf area, and photosynthetic parameters. Our results showed that P. australis exhibited high tolerance to stable and fluctuating water levels up to 30 cm depth. Increased shoot elongation rate and water-use efficiency promoted the establishment of P. australis in flooding habitats. The common reeds in the high-frequency water level fluctuation had a shorter shoot height and a lower shoot density than those in the low-frequency one. The coastal populations performed better under high (30 cm) and low (0 cm) water levels than the inland populations, which preferred shallow water (15 cm). The adaptation strategies of coastal and inland reeds to fluctuation frequencies were no different. We concluded that local adaptation might occur in P. australis populations due to different water levels rather than fluctuation frequency in coastal and inland wetlands. Our findings could provide a theoretical basis on the effects of flooding on intraspecific variation of wetland plants in future environmental change scene.